1. Field of the Invention
The present invention relates to a coating machine to coat material webs, more particularly, material webs made from paper or carton.
2. Description of the Related Art
Reference is made to German patent document DE 3236991 and DE 33111081. It should be noted here that the moving surface which is to be coated is a material web in the case of direct application. In the case of indirect application, the moving surface is an applicator roll which transfers the medium onto the material web.
The machines described in the above-mentioned patent documents require different coater rods for different mediums to be applied, i.e., different coater rods having various diameters and contact pressure characteristics had to be selected to suit different medium viscosities. This required significant machine time and readjustment of the contact pressure onto the material web each time a new coating medium, and therefore a new coater rod, was selected.
In order to achieve a satisfactory coating quality on the material web, it was necessary to pre-meter the medium in significant excess quantities, which subsequently had to be removed by the coater element in order achieve the required coating weight. As a general rule, approximate 90 to 95% of the pre-metered medium had to be removed from the moving surface. In order to be able to handle the excess coating, it was necessary to maintain a high metering pressure in metering chamber. Therefore, this method required high pumping power (for the supply and discharge of the medium). The removal of excess material was typically performed by groo coater rods which, because of their ability to volumetrically meter the medium, were better for the task. However, these rods are more complex to manufacture and maintain. Furthermore, these particular rods are prone to substantially greater wear compared to smooth coater rods.